There is a very large, and still rapidly growing, demand for wireless communication services today. Mobile telephone services are used to a very large extent, e.g. for telephone conversations and text messages. Also, high speed wireless communication is used for a large number of applications, such as internet browsing, streaming of music, films and/or television, and the like.
Since the demand for wireless communication services is very high, and the end users expect the wireless services to be available essentially everywhere they go, the wireless communication system coverage must cover very large geographical areas, both indoors and outdoors, and also provide high bitrates in these areas.
Traditionally, radio base stations, such as Base Transceiver Stations (BTS) and/or NodeBs and/or eNodeBs, hereinafter called Remote Unit Controllers (RUC), are typically located very close to a tower comprising one or more tower-mounted antennas. Said RUCs are provided with all the circuitry necessary for sending and receiving the wireless communication signals to and from the mobile equipments connecting to it, such as Mobile Stations (MS) or User Equipments (UEs). The radio base stations have typically been arranged in cells. The traditional radio base stations include both the circuitry to receive and transmit signals from and to a core network and to receive and transmit signals from and to the one or more antennas, including radio frequency (RF) circuits and power amplifiers, as is illustrated in FIG. 1.
In FIG. 1, the traditional radio base station 101 in a traditional communication system is located close to a tower 102 being connected to a base station 101 by a cable 103, where the cable 103 often is a coaxial cable. The tower 102 has one or more antenna arrangements and the radio base station 101 and the one or more antenna arrangements provide coverage for a cell in the system. The radio base station 101 is connected to the core network 104. In the radio base station 101, circuitry for handling the signaling of the transport layer, the control layer, the synchronization layer, the baseband layer and the radio layer are arranged. Also, power amplifiers are arranged within the radio base station 101. Thus, the radio base station 101 provides RF signals to the antenna in the tower 102. Possibly, a Tower Mounted Amplifier (TMA) is required in the tower 102 due to losses in the cable 103 from the base station circuitry in the radio base station 101 to the one or more antenna arrangements in the tower 102. The cells, each being covered by such a radio base station 101, have traditionally been planned and located side by side with other cells such that an acceptable coverage of a geographical area is achieved. However, since the end users nowadays expect the high speed wireless communication services, such as mobile telecommunication services, wireless fidelity networks (WiFi), and Wireless Local Area Networks (WLANs), to be available essentially everywhere, it would be very costly to build traditional radio base stations at every site where coverage and high bitrates are needed. Also, in indoor locations, such as in malls, railway tunnels, road tunnels, restaurants, cafés, airports, conference centers, tunnels, stadiums and exhibition halls, the traditional radio base station concept results in poor service coverage and bitrates.
To solve this problem, Distributed Antenna Systems (DAS) have been developed. One example of such DAS is schematically disclosed in FIG. 2. Here, one or more Remote Unit Controllers (RUC; 212), each possibly being utilized by one operator/service provider and providing one system and/or service, are being connected to a RUC interface 231. The RUC interface 231 is arranged for providing an interface for one or more RUC 212 and/or one or more fiber cables 230. As mentioned above, typically, the one or more RUCs 212 are radio base stations, such as a BTS or an eNodeB or the like of the type being described above in connection with FIG. 1. These radio base stations provide RF signals to the RUC interface 231. The RUC interface 231 then combines the RF signals from each of the RUs and provides these combined RF signals to one or more fiber cables 230. Thus, the combined RF signals being provided to the fiber cable 230 may include a one or more of RF signals related to a number one or more services and/or service providers. The fiber cable 230 can then distribute the RF signals to one or more Remote Units (RU; 222) and antenna arrangements 228, being located at suitable locations for proving coverage and sufficient bitrates where the demand is.
The DAS concept has a number of advantages. One such advantage is that DAS can be utilized for physically separating the spatially large and power consuming base station circuitry from the one or more antenna arrangements. For example, in environments where the space is limited and/or where power supply is limited or costly to provide, it can be very advantageous to place the RUCs 212 at a location, possibly a central location, where space and power are available, and then distribute the RUs 222 to locations where coverage and high bitrates are needed, but where there is a shortage in space and/or power supply. This also reduces the installation costs, since the more bulky and space consuming RUC can be placed where there is plenty of room, which usually results in a lower rent for the premises.
There are also esthetical advantages in implementation of DAS, since the smaller RUs can easily be designed e.g. to fit into the interior of a mall, an airport or the like. The operation and maintenance costs can also be significantly reduced when DAS is utilized, since maintenance is easier, and therefore also less costly, in one convenient RUC location having more space, and possibly being located centrally, than in a large number of possibly less convenient distributed RU locations.
If the fiber cables 230 are chosen and set up properly, the RUs 222 can be spaced long distances apart from the RUC, functional distances of tens of kilometers can be reached, such that very large geographical areas can be covered by the DAS.
Also, smaller cells have been developed, such as pico cells and femto cells, which can be used for increasing coverage and bitrates, and to lower the costs. The micro base stations and pico base stations are complete standalone radio base stations, including all the circuitry of the traditional radio base stations, including all the circuitry necessary for sending and receiving the wireless communication signals to and from the mobile equipment, however they can be deployed such that coverage and bitrates can be optimized for the geographical area of the communication system, both outdoors and indoors.
A further development of the smaller cell concept is the Remote Radio Head (RRH) concept. The RRH concept breaks up the traditional radio base station architecture into a possibly centrally located processing facility, which in this document will be called RRH controller, and one or more distributed antennas units, in this document called RRH units, being connected to the processing facility through a network preferably having a high bandwidth.
Here, all the traditional radio base station processing equipment except for the radio frequency processing equipment and the power amplification equipment are located in the RRH controller, whereas the radio frequency processing equipment and power amplification equipment are located in the distributed RRH units. An example of the RRH concept is schematically illustrated in FIG. 3.
In FIG. 3, the RRH controller 301 is arranged as a distribution node. The RRH controller 301 can be located centrally in the network and can also be implemented as a base station hotel. In the RRH controller 301, circuitry for handling the signaling of the transport layer, the control layer, the synchronization layer, and the baseband layer is arranged.
The RRH controller 301 is connected to the distributed RRH units 302 by a preferably high bandwidth distribution network 303. The distribution network 303 provides a digital link between the RRH controller 301 and the RRH units 302. The RRH controller 301 is further connected to the core network 304. In the distributed RRH units 302, the radio layer circuitry and power amplifiers are arranged. In FIG. 3, the number of distributed RRH units 302 has been limited to two RRH units 202 to enhance the intelligibility of the figure. However, a large number of distributed RRH units can be connected to the RUCs.
As has been described above, there are today a number of concepts available for extending the coverage of mobile services and for enhancing the bitrates at certain locations in the systems. However, each system working according to these concepts have to be installed, maintained, monitored and controlled. Also, each one of these systems have to be provided with power supplies, distribution networks, locations for mounting radio base stations, RUCs, RRH controllers, towers, RUs, RRH units and antenna arrangements. Thus, to provide sufficient coverage and bitrates today is very costly, and it is also very work and time consuming to monitor and maintain all of these different systems.